Off-grid power calculator

RV Solar & Battery Sizing Calculator

Estimate a starting solar-array size and battery-bank capacity from your daily energy use. The calculator exposes every assumption so you can model cloudy-day margin, different battery chemistries and realistic solar conditions.

Add the watt-hours used by your fridge, lights, fans, electronics, pumps and inverter loads over a typical day.
Use a conservative seasonal value for where and when you camp, not the best summer day.
Allows for controller, wiring, temperature, angle and other real-world losses.
Adds extra array capacity for imperfect weather and usage variation.
How long the battery bank should support the entered daily load without meaningful solar input.
Minimum modeled array—
Array with reserve—
Battery bank—

Formula: minimum solar watts = daily Wh ÷ peak sun hours ÷ system efficiency. Reserve-sized array = minimum array × (1 + reserve margin). Battery Ah = daily Wh × autonomy days ÷ bank voltage ÷ usable-depth fraction.

Start with daily watt-hours, not panel count

A solar setup should be sized from the energy you expect to consume. Two RVs with identical roof area can need completely different systems if one runs only lights and a water pump while the other powers computers, residential refrigeration or inverter loads. Measure or estimate daily watt-hours first, then size generation and storage around that demand.

Peak sun hours are not hours of daylight

Peak sun hours convert changing solar intensity into an equivalent number of full-power hours. A panel does not produce its rated wattage from sunrise to sunset. Trees, clouds, season, latitude, panel temperature and mounting angle all reduce real output. For planning, using a conservative sun-hour assumption is more useful than designing around a perfect summer day.

Why the calculator includes efficiency losses

Panel nameplate wattage is a laboratory rating. Real RV systems lose energy through heat, controller conversion, wiring, shading, dirt and battery charging. The default 75% system efficiency is a planning assumption, not a universal truth. If you have measured production from your own installation, replace it with a more accurate value.

Battery chemistry changes required capacity

A battery bank advertised as 200 Ah does not necessarily provide 200 Ah of practical usable capacity. This calculator models LiFePO4 at 80% usable and AGM/lead-acid at 50% usable by default. Those are planning values; battery manufacturers specify their own limits, warranties and recommended depth of discharge.

Roof space can become the real bottleneck

The calculated array may be larger than the usable roof area. Air conditioners, vents, antennas and shading can reduce mounting space substantially. If the roof cannot support the target wattage, portable panels, alternator charging, shore power or reduced energy demand can fill the gap.

Use measured loads before spending thousands

For a high-cost build, measure actual appliance consumption with a battery monitor or power meter over several representative days. A precise measurement of demand is more valuable than adding another panel to compensate for a bad estimate.

Next: compare your result with our RV Battery Runtime Calculator, then read How Much Solar Do I Need for an RV? for the system-design trade-offs.